This application is based upon and claims priority to German Patent Application 199 46 824.9 filed Sep. 30, 1999, which application is herein expressly incorporated by reference.
The present invention relates to a wiper rest heater for de-icing frozen or snowed-in windshield wipers.
When temperatures are low, the windshield wiper blade elements can, on occasion, freeze to the windshield, particularly when parking overnight in exposed places. If the driver of the vehicle then switches the windshield wiper on, to clear the shield for example, then either the motor can be blocked and damaged or the windshield wiper blade elements can be damaged as they break free.
Therefore, in the case of previous vehicles, the area of the windshield on which the windshield wiper/s is/are located in the rest position is heated by a wiper rest heater. The heating enables the frozen-on wiper to be freed. The criterion for switching on is the external temperature and the ignition being switched on. If the external temperature falls below a specific limiting value then, if the ignition is switched on, the wiper rest heater is switched on irrespective of whether the wiper is frozen-on or not. However, the disadvantage of this is that the heating requires several hundred watts of electrical power, thus significantly increasing the fuel consumption because the heating always remains switched on or at least remains on for a specific time, no matter whether this is necessary or not.
DE 42 35 114 A1 discloses a motor vehicle with a windshield, in which the windshield wipers of a motor vehicle are arranged in the cowling which is located on the lower edge of a windshield. A separate air ducting channel is provided on the inside of the vehicle which directs warm air to the wiper rest area of the windshield wipers in order to free iced-up or snowed-in windshield wipers. A ribbed heat-transfer body, which is connected to the windshield via an adhesive layer with high thermal conductivity, is arranged on the inside of the windshield in the area of the hot air outlet in order to improve the heat transfer to the windshield.
However, the disadvantages of this are that the de-icing of the windshield wiper takes a relatively long time, and the heater heats the wiper rest even when the windshield wipers are not frozen to the windshield or covered with snow. The heater is automatically switched on together with the ventilation in the interior of the vehicle.
The object of the invention is to provide a reduction of the energy consumption of a wiper rest heater of the type mentioned at the beginning, which is needed to ensure that the windshield wipers also function properly at low temperatures and to speed up thawing times.
In accordance with the invention this task is solved by the wiper rest heater connected to a sensor which measures whether the windshield wipers move or not while the windshield wiper motor is switched on. This information is then evaluated in an evaluation unit. With the result that the wiper rest heater is then switched on and off in such a way that the wiper rest heater is only then switched on if the windshield wipers are actually frozen.
A further advantage is achieved by a revolution sensor on the wiper motor which is used as a sensor, or it is designed as an ammeter which measures the current through the wiper motor. The sensor can also be designed as a movement sensor which directly measures the movement of the windshield wipers.
The advantages achieved with the invention are exact switching on of the wiper rest heater, which is only switched on when it is actually needed, that is, only when the windshield wipers are actually frozen and can no longer be moved. In the same way, it can also be switched off exactly, namely precisely when the thawing process has ended.
From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.